Predictors of Tooth Loss in Patients Wearing a Partial Removable Dental Prosthesis Yoko Mizuno, DDS, PhD1/Ross Bryant, BSc, DDS, MSc, PhD2/Tomoya Gonda, DDS, PhD3
Purpose: The partial removable dental prosthesis (PRDP) is used widely to replace missing teeth, but it can disturb the ecology of the mouth. In this retrospective cohort study, the null hypothesis was that there was no difference between tooth loss and the type of edentulous spaces in participants wearing PRDPs. Materials and Methods: Participants were selected from patients who were treated consecutively with PRDPs between January 2003 and December 2006 by undergraduate dental students at the University of British Columbia and attended the clinic for at least 5 years following placement of the PRDP. Clinical records were analyzed for 50 men and 52 women aged 19 to 85 years at baseline, before placement of the PRDP (mean age: 63.2 years). Baseline data were obtained from the records on missing teeth and edentulous spaces, and thereafter data were collected on teeth lost over the following 5-year period. Baseline data on age, sex, occlusal contacts, number of dental rests for the dentures, carious teeth, gingival attachment loss, and teeth with endodontic fillings were also obtained. Results: The presence at baseline of teeth with endodontic fillings significantly (P < .05) increased the prediction of tooth loss over the 5 years, but the type of edentulous space did not. Conclusion: The risk of tooth loss over a 5-year period was higher in the presence of endodontically treated teeth, but no higher in participants wearing PRDPs with distally extended edentulous spaces rather than tooth-bounded edentulous spaces. Int J Prosthodont 2016;29:399–402. doi: 10.11607/ijp.4630
T
ooth loss is a major disability worldwide, commonly caused by caries, periodontal disease, and trauma.1–4 Partial removable dental prostheses (PRDPs) are used widely to replace missing teeth and are reported to have a high survival rate and a low rate of extraction of abutment teeth.5 However, PRDPs can disturb the ecology of the mouth and increase the incidence of caries and periodontal disease.6,7 Gonda et al found a significant association between tooth loss and several personal and biologic factors but concluded that use of a denture was the strongest predictor of tooth loss over 5 years.8 Another retrospective study over 15 years concluded that abutment teeth for a PRDP were at greater risk than
other teeth for extraction.9 Others reported that direct and indirect retainers on dentures caused periodontal damage over time and that periodontal pockets were deeper around the teeth adjacent to a distally extended (DE) edentulous space when compared with a tooth-bounded (TB) space.10,11 Consequently, the design of the denture and the type of edentulous spaces could influence the survival of the remaining teeth. However, no studies have analyzed the potential relationship between the type of edentulous spaces and tooth loss. In this retrospective cohort study, the null hypothesis was that there was no difference between tooth loss and the type of edentulous spaces in participants wearing PRDPs.
Materials and Methods 1Resident,
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Osaka, Japan. 2Assistant Professor, Department of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada. 3Associate Professor, Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Osaka, Japan. Correspondence to: Dr Tomoya Gonda, Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan. Fax: +81-6-6879-2957. Email: [email protected] ©2016 by Quintessence Publishing Co Inc.
Clinical records for 50 men and 52 women aged 19 to 85 years (mean age at baseline: 63.2 years) treated at a university-based dental clinic (Nobel Biocare Oral Health Centre, Vancouver, Canada) by undergraduate dental students were analyzed to identify the predictors of tooth loss over 5 years. A sample of 513 participants was selected from among patients treated consecutively with PRDPs between January 2003 and December 2006, excluding 393 patients who did not attend the clinic continuously for the full 5 years and 18 patients for whom the necessary data was not available. Collectively, 102 participants had 73 DE-PRDPs
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Predictors of Tooth Loss
Table 1 Characteristics of Participants at Baseline Denture design Distally extended Tooth-bounded Combined Characteristic
n
%
n
Sex Men 36 49.3 16 Women 37 50.7 22 Age at baseline (y) < 65 31 42.5 18 ≥ 65 42 57.5 20 Teeth with caries (n) 0 40 54.8 18 ≥1 33 45.2 20 Teeth with attachment loss ≥ 6 mm (n) 0 13 17.8 7 1 6 8.2 8 ≥2 54 74.0 23 Endodontically treated teeth (n) 0 40 54.8 12 ≥1 33 45.2 26 Eichner classification A 0 0.0 9 B 43 58.9 23 C 30 41.1 6 Arch with denture Maxilla 21 28.8 23 Mandible 52 71.2 15 Dental rests (n) ≤2 23 31.5 1 3 29 39.7 12 ≥4 21 28.8 25
%
n
42.1 57.9
52 59
47.4 52.6
49 62
47.4 52.6
58 53
18.4 21.1 60.5
20 14 77
31.6 68.4
52 59
23.7 60.5 15.8
9 66 36
60.5 39.5
43 67
2.6 31.6 65.8
24 41 46
(31 bilateral and 42 unilateral) and 38 TB-PRDPs (3 with TB spaces in the anterior sextant). The 73 DEPRDPs included 9 horseshoe bars, 9 palatal bars, 3 palatal plates, 6 lingual bars, and 46 lingual plates. The 38 TB-PRDPs included 10 horseshoe bars, 11 palatal bars, 2 palatal plates, 3 lingual bars, and 12 lingual plates. For each participant, the missing teeth at baseline before dentures were inserted were documented, along with age, sex, Eichner classification of occlusal contacts without dentures, the type of edentulous spaces (DE or TB), and the number of dental rests on the PRDP. Eichner classification12–16 is determined by the occlusal contacts involving natural teeth or fixed partial dentures in the premolar and molar areas. Class A has contacts in four support areas, Class B has contact in one to three areas or in the anterior area only, and Class C has no support area with occlusal contacts at all, although a few teeth can still remain. The baseline number was also recorded of teeth with caries (by visual inspection), attachment loss (AL) ≥ 6 mm from the cementoenamel junction vertically
400
to the gingival attachment (by measuring periodontal pocket depth and gingival recession), and endodontic fillings. Thereafter, the number of teeth extracted over the following 5-year period was recorded. The study was approved by the Clinical Research Ethics Board of the University of British Columbia (H12-03350). Data Analysis The data were analyzed using SPSS version 11.0.1 (IBM) with a threshold significance at P < .05 for bivariate and multivariate analyses to identify predictors of tooth loss. Chi-square test for bivariate analysis was used to determine the specific relationship between tooth loss over the 5 years and each variable. Data were analyzed for three groups: (1) all the participants, (2) participants with DE dentures, and (3) participants with TB dentures. Nine participants had two dentures. Binary logistic multiple regression (BLMR) was used to test associations between tooth loss and potential predictors in each group. The independent variable was whether at least one tooth was lost over the 5-year period. The baseline explanatory variables were as follows: sex (men vs women), age (< 65 years vs ≥ 65 years), teeth with caries (0 vs ≥ 1), teeth with AL ≥ 6 mm (0 or 1 vs ≥ 2), teeth with endodontic treatment (0 vs ≥ 1), arch with denture (maxilla vs mandible), type of edentulous area (DE vs TB), Eichner classification (A or B vs C), number of dental rests (1 or 2 vs ≥ 3).
Results Baseline Distributions There were 73 participants in the DE group and 38 participants in the TB group. At baseline, most of them were free of caries, had ≥ 2 teeth with AL ≥ 6 mm, had ≥ 1 endodontic filling, and were Eichner Type B (Table 1). Dentures were predominantly mandibular DE-PRDPs, and had four or more dental rests. Bivariate Analysis Over one-third of participants lost at least one tooth during the study period (Table 2). Overall tooth loss was associated only with participants who had endodontic fillings, but not all extracted teeth had prior endodontic treatment. Furthermore, tooth loss in the TB group was associated both with AL ≥ 6 mm at baseline and the denture being in the maxillary arch, whereas tooth loss in the DE group was only associated with participants having an endodontic filling at baseline.
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Mizuno et al
Multivariate Analysis The odds ratio (OR) of tooth loss associated with the presence of endodontic fillings was 2.93 in the allparticipant group and 6.30 in the DE group, which emphasized the strength of predicting tooth loss in participants with DEs and endodontically treated teeth (Tables 3 and 4). Tooth loss in the DE group was also associated with being aged at least 65 years, with an OR of 3.76 (Table 4).
Discussion The lack of association between tooth loss and attachment loss or caries was surprising and in contrast to previous studies,8,17–21 probably because the participants of the present study received careful maintenance care during the study period. The present results are consistent with previous studies showing the possible vulnerability of endodontically treated teeth, or at least that PRDP patients with a history of endodontic treatment have an elevated risk of tooth loss whether or not the specific teeth lost had prior endodontic treatment.9,22 Nonetheless, the present study found that tooth loss frequently occurred where an endodontically treated root fractured.23,24 Ostensibly, the load and stress induced by a DE when combined with the structural weakness of endodontically treated teeth predisposes and predicts further problems and an increased risk of tooth loss.25–27 All the DE dentures were made with a double (alteredcast) impression technique, so the ability of this clinical method to reduce the load of a denture on a distal extension needs further investigation. The influence of age on tooth loss is controversial. Some investigations suggest that they are not associated,19,21 whereas several others found a significant association.4,5,20,21 The present study found the association only in the DE group, where stress from dentures on abutment teeth, as has been explained, probably had a greater effect than in the TB group or the combined group of all participants. Previous studies1–4 concluded that the main reasons for extracting teeth are caries and, to a lesser extent, periodontal disease. This study found that neither caries nor attachment loss ≥ 6 mm predicted tooth loss in multivariate analysis. Sato et al found that periodontal pocket depth and bone levels around the teeth deteriorated significantly adjacent to a DE edentulous space, much more than around teeth adjacent to tooth-bounded spaces.11 In contrast, Bergman et al found little or no loss of teeth or change in periodontal condition during a similar study of minimally invasive dentures for patients who were maintained carefully with frequent clinical assessments and dental
Table 2 N umber of Teeth Extracted in the 5 Years After Dentures Were Inserted Teeth extracted (n)
Distally extended Tooth-bounded
0 1 ≥2
Combined
n
%
n
%
n
%
44 15 14
60.3 20.5 19.2
25 11 2
65.8 28.9 5.3
69 26 16
62.2 23.4 14.4
Table 3 M ultivariate Models Using Logistic Regression to Predict Tooth Loss in the All-Participant Group Predictor Sex Age at baseline (y) Teeth with caries (n)
B
SE
Odds ratio (95% CI)
P
−0.26
0.44
0.77 (0.33–1.81)
.55
0.63
0.46
1.88 (0.77–4.59)
.16
0.3
0.44
1.34 (0.57–3.15)
.5
−0.57
0.47
0.56 (0.22–1.43)
.23
1.07
0.51
2.93 (1.07–8.01)
*.04
Eichner classification
−0.18
0.52
0.84 (0.30–2.34)
.74
Arch with denture
Teeth with attachment loss ≥ 6 mm (n) Endodontically treated teeth (n)
−0.57
0.48
0.57 (0.22–1.45)
.24
Dental rests (n)
0.26
0.57
1.25 (0.41–3.81)
.69
Denture design
−0.61
0.5
0.54 (0.20–1.46)
.24
SE = standard error; CI = confidence interval. *P < .05.
Table 4 M ultivariate Models Using Logistic Regression to Predict Tooth Loss in the Distally Extended PRDP Group B
SE
Odds ratio (95% CI)
P
−0.15
0.56
0.86 (0.29–2.59)
.79
Age at baseline (y)
1.33
0.63
3.77 (1.09–13.0)
*.04
Teeth with caries (n)
0.6
0.59
1.82 (0.58–5.72)
.31
Teeth with attachment loss ≥ 6 mm (n)
−0.12
0.62
0.89 (0.26–3.03)
.85
Endodontically treated teeth (n)
1.84
0.74
6.30 (1.48–26.8)
*.01
Predictor Sex
Eichner classification
−0.45
0.7
0.64 (0.16–2.50)
.52
Arch with denture
−0.04
0.66
0.96 (0.26–3.54)
.96
0.5
0.64
1.65 (0.47–5.74)
.43
Dental rests (n)
SE = standard error; CI = confidence interval. *P < .05.
hygiene.28 The present authors believe that the patients attending the university-based clinic received similarly designed dentures and after care, although over one-third of the participants lost teeth. The limitations of the study were exclusion of patients who did not return for care for the full 5 years, which likely biased the results in favor of participants who are more compliant with advice on preventing
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Predictors of Tooth Loss
further tooth loss. It was also difficult to find and understand pertinent details in some of the clinical records; however, it was usually possible to extract data on the major variables for analysis. Patients attending a dental school clinic might not accurately represent patients who attend dentists in general practice. However, it is not clear exactly how they might differ, other than perhaps by the financial barriers they encounter to paying for prosthodontic treatment as fees paid at the dental school were known to be substantially lower than those found in general practice. There is good evidence that tooth loss is more closely associated with lower socioeconomic status in contrast to higher.18,29,30 The small sample size, especially in the TB group, was a limitation of this study, raising the possibility of type II error.
Conclusions The presence of endodontically treated teeth at baseline was significantly associated with tooth loss in this cohort of participants, while the denture design, whether for distally extended or tooth-bounded edentulous spaces, had no significant influence.
Acknowledgments The authors thank the staff of the Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry. The authors also wish to express their gratitude to Professor Michael I. MacEntee (Vancouver, British Columbia, Canada) and Professor Yoshinobu Maeda (Osaka, Japan). This work was supported by the Osaka University Scholarship for Shortterm Overseas Research Activities 2010 from Osaka University. The authors reported no conflicts of interest related to this study.
References 1. Ainamo J, Sarkki L, Kuhalampi ML, Palolampi L, Piirto O. The frequency of periodontal extractions in Finland. Community Dent Health 1984;1:165–172. 2. Stephens RG, Kogon SL, Jarvis AM. A study of the reasons for tooth extraction in a Canadian population sample. J Can Dent Assoc 1991;57:501–504. 3. Nevalainen MJ, Narhi TO, Siukosaari P, Schmidt-Kaunisaho K, Ainamo A. Prosthetic rehabilitation in the elderly inhabitants of Helsinki, Finland. J Oral Rehabil 1996;23:722–728. 4. Matsuda K, Ikebe K, Enoki K, Tada S, Fujiwara K, Maeda Y. Incidence and association of root fractures after prosthetic treatment. J Prosthodont Res 2011;55:137–140. 5. Rehmann P, Orbach K, Ferger P, Wöstmann B. Treatment outcomes with removable partial dentures: A retrospective analysis. Int J Prosthodont 2013;26:147–150. 6. Wagner B, Kern M. Clinical evaluation of removable partial dentures 10 years after insertion: Success rates, hygienic problems, and technical failures. Clin Oral Investig 2000;4:74–80. 7. MacEntee MI. Biologic sequelae of tooth replacement with removable partial dentures: A case for caution. J Prosthet Dent 1993;70:132–134.
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8. Gonda T, MacEntee MI, Kiyak HA, Persson GR, Persson RE, Wyatt C. Predictors of multiple tooth-loss among socio-culturally diverse elderly subjects. Int J Prosthodont 2013;26:127–134. 9. Miyamoto T, Morgano SM, Kumagai T, Jones JA, Nunn ME. Treatment history of teeth in relation to the longevity of the teeth and their restorations: Outcomes of teeth treated and maintained for 15 years. J Prosthet Dent 2007;97:150–156. 10. do Amaral BA, Barreto AO, Gomes Seabra E, Roncalli AG, da Fonte Porto Carreiro A, de Almeida EO. A clinical follow-up study of the periodontal conditions of RPD abutment and nonabutment teeth. J Oral Rehabil 2010;37:545–552. 11. Sato F, Koyama S, Takahiro C, Kadowaki K, Tetsuo K, Sasaki K. Changes in periodontal conditions of remaining teeth five years after RPD placement. Ann Jpn Prosthodontic Soc 2009;1:130–138. 12. Yoshino K, Kikukawa I, Yoda Y, et al. Relationship between Eichner Index and number of present teeth. Bull Tokyo Dent Coll 2012;53:37–40. 13. Hiltunen K, Vehkalahti MM, Peltola JS, Ainamo A. A 5-year follow-up of occlusal status and radiographic findings in mandibular condyles of the elderly. Int J Prosthodont 2002;15:539–543. 14. Ikebe K, Hazeyama T, Iwase K, et al. Association of symptomless TMJ sounds with occlusal force and masticatory performance in older adults. J Oral Rehabil 2008;35:317–323. 15 Eichner K. Über eine gruppeneinteilung der lückengebisse für der prothetik. Dtsch Zahnärztl Z 1955;10:1831–1834. 16. Eichner K. Renewed examination of the group classification of partially edentulous arches by Eichner and application advices for studies on morbidity statistics [in German]. Stomatol DDR 1990; 40:321–325. 17. Seida Y, Yoshihara A, Ando Y, Miyazaki H. Two-year cohort study on risk predictors for tooth loss in residing in the community 70-year-old subjects. Journal of Dental Health 2002;52:663–671. 18. Burt BA, Ismail AI, Morrison EC, Beltran ED. Risk factors for tooth loss over a 28-year period. J Dent Res 1990;69:1126–1130. 19. Locker D, Ford J, Leake JL. Incidence of and risk factors for tooth loss in a population of older Canadians. J Dent Res 1996; 75:783–789. 20. Baelum V, Luan WM, Chen X, Fejerskov O. Predictors of tooth loss over 10 years in adult and elderly Chinese. Community Dent Oral Epidemiol 1997;25:204–210. 21. Warren JJ, Watkins CA, Cowen HJ, Hand JS, Levy SM, Kuthy RA. Tooth loss in the very old: 13-15-year incidence among elderly Iowans. Community Dent Oral Epidemiol 2002;30:29–37. 22. Kawamura Y, Shinsho F, Hideki F. Factors related to tooth loss during a long-term maintenance program at dental clinics. J Dent Health 2007;57:159–165. 23. Axelsson P, Nyström B, Lindhe J. The long-term effect of a plaque control program on tooth mortality, caries and periodontal disease in adults. Results after 30 years of maintenance. J Clin Periodontol 2004;31:749–757. 24. Cohen S, Berman LH, Blanco L, Bakland L, Kim JS. A demographic analysis of vertical root fractures. J Endod 2006;32:1160–1163. 25. Pegoretti A, Fambri L, Zappini G, Bianchetti M. Finite element analysis of a glass fibre reinforced composite endodontic post. Biomaterials 2002;23:2667–2682. 26. Ukon S, Moroi H, Okimoto K, et al. Influence of different elastic moduli of dowel and core on stress distribution in root. Dent Mater J 2000;19:50–64. 27. Santos AF, Meira JB, Tanaka CB, et al. Can fiber posts increase root stresses and reduce fracture? J Dent Res 2010;89:587–591. 28. Bergman B, Hugoson A, Olsson CO. A 25 year longitudinal study of patients treated with removable partial dentures. J Oral Rehabil 1995;22:595–599. 29. Klein BE, Klein R, Knudtson MD. Life-style correlates of tooth loss in an adult Midwestern population. J Public Health Dent 2004;64:145–150. 30. MacEntee MI, Hill PM, Wong G, Mojon P, Berkowitz J, Glick N. Predicting concerns for the mouth among institutionalized elders. J Public Health Dent 1991;51:82–90.
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Purpose: The partial removable dental prosthesis (PRDP) is used widely to replace missing teeth, but it can disturb the ecology of the mouth. In this retrospective cohort study, the null hypothesis was that there was no difference between tooth loss and the type of edentulous spaces in participants wearing PRDPs. Materials and Methods: Participants were selected from patients who were treated consecutively with PRDPs between January 2003 and December 2006 by undergraduate dental students at the University of British Columbia and attended the clinic for at least 5 years following placement of the PRDP. Clinical records were analyzed for 50 men and 52 women aged 19 to 85 years at baseline, before placement of the PRDP (mean age: 63.2 years). Baseline data were obtained from the records on missing teeth and edentulous spaces, and thereafter data were collected on teeth lost over the following 5-year period. Baseline data on age, sex, occlusal contacts, number of dental rests for the dentures, carious teeth, gingival attachment loss, and teeth with endodontic fillings were also obtained. Results: The presence at baseline of teeth with endodontic fillings significantly (P < .05) increased the prediction of tooth loss over the 5 years, but the type of edentulous space did not. Conclusion: The risk of tooth loss over a 5-year period was higher in the presence of endodontically treated teeth, but no higher in participants wearing PRDPs with distally extended edentulous spaces rather than tooth-bounded edentulous spaces. Int J Prosthodont 2016;29:399–402. doi: 10.11607/ijp.4630
T
ooth loss is a major disability worldwide, commonly caused by caries, periodontal disease, and trauma.1–4 Partial removable dental prostheses (PRDPs) are used widely to replace missing teeth and are reported to have a high survival rate and a low rate of extraction of abutment teeth.5 However, PRDPs can disturb the ecology of the mouth and increase the incidence of caries and periodontal disease.6,7 Gonda et al found a significant association between tooth loss and several personal and biologic factors but concluded that use of a denture was the strongest predictor of tooth loss over 5 years.8 Another retrospective study over 15 years concluded that abutment teeth for a PRDP were at greater risk than
other teeth for extraction.9 Others reported that direct and indirect retainers on dentures caused periodontal damage over time and that periodontal pockets were deeper around the teeth adjacent to a distally extended (DE) edentulous space when compared with a tooth-bounded (TB) space.10,11 Consequently, the design of the denture and the type of edentulous spaces could influence the survival of the remaining teeth. However, no studies have analyzed the potential relationship between the type of edentulous spaces and tooth loss. In this retrospective cohort study, the null hypothesis was that there was no difference between tooth loss and the type of edentulous spaces in participants wearing PRDPs.
Materials and Methods 1Resident,
Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Osaka, Japan. 2Assistant Professor, Department of Oral Health Sciences, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada. 3Associate Professor, Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, Osaka, Japan. Correspondence to: Dr Tomoya Gonda, Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan. Fax: +81-6-6879-2957. Email: [email protected] ©2016 by Quintessence Publishing Co Inc.
Clinical records for 50 men and 52 women aged 19 to 85 years (mean age at baseline: 63.2 years) treated at a university-based dental clinic (Nobel Biocare Oral Health Centre, Vancouver, Canada) by undergraduate dental students were analyzed to identify the predictors of tooth loss over 5 years. A sample of 513 participants was selected from among patients treated consecutively with PRDPs between January 2003 and December 2006, excluding 393 patients who did not attend the clinic continuously for the full 5 years and 18 patients for whom the necessary data was not available. Collectively, 102 participants had 73 DE-PRDPs
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Predictors of Tooth Loss
Table 1 Characteristics of Participants at Baseline Denture design Distally extended Tooth-bounded Combined Characteristic
n
%
n
Sex Men 36 49.3 16 Women 37 50.7 22 Age at baseline (y) < 65 31 42.5 18 ≥ 65 42 57.5 20 Teeth with caries (n) 0 40 54.8 18 ≥1 33 45.2 20 Teeth with attachment loss ≥ 6 mm (n) 0 13 17.8 7 1 6 8.2 8 ≥2 54 74.0 23 Endodontically treated teeth (n) 0 40 54.8 12 ≥1 33 45.2 26 Eichner classification A 0 0.0 9 B 43 58.9 23 C 30 41.1 6 Arch with denture Maxilla 21 28.8 23 Mandible 52 71.2 15 Dental rests (n) ≤2 23 31.5 1 3 29 39.7 12 ≥4 21 28.8 25
%
n
42.1 57.9
52 59
47.4 52.6
49 62
47.4 52.6
58 53
18.4 21.1 60.5
20 14 77
31.6 68.4
52 59
23.7 60.5 15.8
9 66 36
60.5 39.5
43 67
2.6 31.6 65.8
24 41 46
(31 bilateral and 42 unilateral) and 38 TB-PRDPs (3 with TB spaces in the anterior sextant). The 73 DEPRDPs included 9 horseshoe bars, 9 palatal bars, 3 palatal plates, 6 lingual bars, and 46 lingual plates. The 38 TB-PRDPs included 10 horseshoe bars, 11 palatal bars, 2 palatal plates, 3 lingual bars, and 12 lingual plates. For each participant, the missing teeth at baseline before dentures were inserted were documented, along with age, sex, Eichner classification of occlusal contacts without dentures, the type of edentulous spaces (DE or TB), and the number of dental rests on the PRDP. Eichner classification12–16 is determined by the occlusal contacts involving natural teeth or fixed partial dentures in the premolar and molar areas. Class A has contacts in four support areas, Class B has contact in one to three areas or in the anterior area only, and Class C has no support area with occlusal contacts at all, although a few teeth can still remain. The baseline number was also recorded of teeth with caries (by visual inspection), attachment loss (AL) ≥ 6 mm from the cementoenamel junction vertically
400
to the gingival attachment (by measuring periodontal pocket depth and gingival recession), and endodontic fillings. Thereafter, the number of teeth extracted over the following 5-year period was recorded. The study was approved by the Clinical Research Ethics Board of the University of British Columbia (H12-03350). Data Analysis The data were analyzed using SPSS version 11.0.1 (IBM) with a threshold significance at P < .05 for bivariate and multivariate analyses to identify predictors of tooth loss. Chi-square test for bivariate analysis was used to determine the specific relationship between tooth loss over the 5 years and each variable. Data were analyzed for three groups: (1) all the participants, (2) participants with DE dentures, and (3) participants with TB dentures. Nine participants had two dentures. Binary logistic multiple regression (BLMR) was used to test associations between tooth loss and potential predictors in each group. The independent variable was whether at least one tooth was lost over the 5-year period. The baseline explanatory variables were as follows: sex (men vs women), age (< 65 years vs ≥ 65 years), teeth with caries (0 vs ≥ 1), teeth with AL ≥ 6 mm (0 or 1 vs ≥ 2), teeth with endodontic treatment (0 vs ≥ 1), arch with denture (maxilla vs mandible), type of edentulous area (DE vs TB), Eichner classification (A or B vs C), number of dental rests (1 or 2 vs ≥ 3).
Results Baseline Distributions There were 73 participants in the DE group and 38 participants in the TB group. At baseline, most of them were free of caries, had ≥ 2 teeth with AL ≥ 6 mm, had ≥ 1 endodontic filling, and were Eichner Type B (Table 1). Dentures were predominantly mandibular DE-PRDPs, and had four or more dental rests. Bivariate Analysis Over one-third of participants lost at least one tooth during the study period (Table 2). Overall tooth loss was associated only with participants who had endodontic fillings, but not all extracted teeth had prior endodontic treatment. Furthermore, tooth loss in the TB group was associated both with AL ≥ 6 mm at baseline and the denture being in the maxillary arch, whereas tooth loss in the DE group was only associated with participants having an endodontic filling at baseline.
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Mizuno et al
Multivariate Analysis The odds ratio (OR) of tooth loss associated with the presence of endodontic fillings was 2.93 in the allparticipant group and 6.30 in the DE group, which emphasized the strength of predicting tooth loss in participants with DEs and endodontically treated teeth (Tables 3 and 4). Tooth loss in the DE group was also associated with being aged at least 65 years, with an OR of 3.76 (Table 4).
Discussion The lack of association between tooth loss and attachment loss or caries was surprising and in contrast to previous studies,8,17–21 probably because the participants of the present study received careful maintenance care during the study period. The present results are consistent with previous studies showing the possible vulnerability of endodontically treated teeth, or at least that PRDP patients with a history of endodontic treatment have an elevated risk of tooth loss whether or not the specific teeth lost had prior endodontic treatment.9,22 Nonetheless, the present study found that tooth loss frequently occurred where an endodontically treated root fractured.23,24 Ostensibly, the load and stress induced by a DE when combined with the structural weakness of endodontically treated teeth predisposes and predicts further problems and an increased risk of tooth loss.25–27 All the DE dentures were made with a double (alteredcast) impression technique, so the ability of this clinical method to reduce the load of a denture on a distal extension needs further investigation. The influence of age on tooth loss is controversial. Some investigations suggest that they are not associated,19,21 whereas several others found a significant association.4,5,20,21 The present study found the association only in the DE group, where stress from dentures on abutment teeth, as has been explained, probably had a greater effect than in the TB group or the combined group of all participants. Previous studies1–4 concluded that the main reasons for extracting teeth are caries and, to a lesser extent, periodontal disease. This study found that neither caries nor attachment loss ≥ 6 mm predicted tooth loss in multivariate analysis. Sato et al found that periodontal pocket depth and bone levels around the teeth deteriorated significantly adjacent to a DE edentulous space, much more than around teeth adjacent to tooth-bounded spaces.11 In contrast, Bergman et al found little or no loss of teeth or change in periodontal condition during a similar study of minimally invasive dentures for patients who were maintained carefully with frequent clinical assessments and dental
Table 2 N umber of Teeth Extracted in the 5 Years After Dentures Were Inserted Teeth extracted (n)
Distally extended Tooth-bounded
0 1 ≥2
Combined
n
%
n
%
n
%
44 15 14
60.3 20.5 19.2
25 11 2
65.8 28.9 5.3
69 26 16
62.2 23.4 14.4
Table 3 M ultivariate Models Using Logistic Regression to Predict Tooth Loss in the All-Participant Group Predictor Sex Age at baseline (y) Teeth with caries (n)
B
SE
Odds ratio (95% CI)
P
−0.26
0.44
0.77 (0.33–1.81)
.55
0.63
0.46
1.88 (0.77–4.59)
.16
0.3
0.44
1.34 (0.57–3.15)
.5
−0.57
0.47
0.56 (0.22–1.43)
.23
1.07
0.51
2.93 (1.07–8.01)
*.04
Eichner classification
−0.18
0.52
0.84 (0.30–2.34)
.74
Arch with denture
Teeth with attachment loss ≥ 6 mm (n) Endodontically treated teeth (n)
−0.57
0.48
0.57 (0.22–1.45)
.24
Dental rests (n)
0.26
0.57
1.25 (0.41–3.81)
.69
Denture design
−0.61
0.5
0.54 (0.20–1.46)
.24
SE = standard error; CI = confidence interval. *P < .05.
Table 4 M ultivariate Models Using Logistic Regression to Predict Tooth Loss in the Distally Extended PRDP Group B
SE
Odds ratio (95% CI)
P
−0.15
0.56
0.86 (0.29–2.59)
.79
Age at baseline (y)
1.33
0.63
3.77 (1.09–13.0)
*.04
Teeth with caries (n)
0.6
0.59
1.82 (0.58–5.72)
.31
Teeth with attachment loss ≥ 6 mm (n)
−0.12
0.62
0.89 (0.26–3.03)
.85
Endodontically treated teeth (n)
1.84
0.74
6.30 (1.48–26.8)
*.01
Predictor Sex
Eichner classification
−0.45
0.7
0.64 (0.16–2.50)
.52
Arch with denture
−0.04
0.66
0.96 (0.26–3.54)
.96
0.5
0.64
1.65 (0.47–5.74)
.43
Dental rests (n)
SE = standard error; CI = confidence interval. *P < .05.
hygiene.28 The present authors believe that the patients attending the university-based clinic received similarly designed dentures and after care, although over one-third of the participants lost teeth. The limitations of the study were exclusion of patients who did not return for care for the full 5 years, which likely biased the results in favor of participants who are more compliant with advice on preventing
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Predictors of Tooth Loss
further tooth loss. It was also difficult to find and understand pertinent details in some of the clinical records; however, it was usually possible to extract data on the major variables for analysis. Patients attending a dental school clinic might not accurately represent patients who attend dentists in general practice. However, it is not clear exactly how they might differ, other than perhaps by the financial barriers they encounter to paying for prosthodontic treatment as fees paid at the dental school were known to be substantially lower than those found in general practice. There is good evidence that tooth loss is more closely associated with lower socioeconomic status in contrast to higher.18,29,30 The small sample size, especially in the TB group, was a limitation of this study, raising the possibility of type II error.
Conclusions The presence of endodontically treated teeth at baseline was significantly associated with tooth loss in this cohort of participants, while the denture design, whether for distally extended or tooth-bounded edentulous spaces, had no significant influence.
Acknowledgments The authors thank the staff of the Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry. The authors also wish to express their gratitude to Professor Michael I. MacEntee (Vancouver, British Columbia, Canada) and Professor Yoshinobu Maeda (Osaka, Japan). This work was supported by the Osaka University Scholarship for Shortterm Overseas Research Activities 2010 from Osaka University. The authors reported no conflicts of interest related to this study.
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